1. Field of the Invention
The present invention relates to communications networks. More specifically, the present invention relates to the establishment of communications between parties on a communications network with out-of-band call control signaling.
2. Description of Related Art
Currently, many communication systems use out-of-band call control signaling, which separates the call control portion of the bandwidth from the data portion of a call. The call control portion, which is also known as the call control "layer," is separated from the call data layer to allow the controlling and modification of a call even after a call is in progress. Having a separate control layer also allows the conservation of bandwidth before a call is set-up as the bandwidth needed by the control layer is much smaller than the bandwidth of the data layer. Thus, if a call is not set-up for any reason, the bandwidth reserved for the call data layer is not utilized and only the bandwidth used for the control layer has been used. In addition, a separate call control layer allows more call control capabilities to be implemented as the call control signals are not combined with call data signals.
The call data layer is also referred to as a "bearer" channel, and can be configured for different capabilities. For example, a bearer channel can be voice only, which means that the bearer channel cannot carry other types of data. Alternatively, a bearer channel can be voice and data, which means the bearer channel can carry both voice and data traffic. It is important to know the capabilities of the bearer channel, so that the bearer channel can be used to its full capacity. In addition, a low layer capability (LLC) set of indicators and a high layer capability (HLC) set of indicators are used to describe the different parameters of the communication session.
LLC has information such as the number of stop bits, the number of start bits, and parity bits that are used by the bearer channel. HLC has information such as the coding standard of the data to be exchanged, interpretation information, and protocol information.
An exemplary communication system that uses separate layers for control and data is the integrated services digital network (ISDN) system. The definition of the capabilities of each participation in a communication session is contained in the ISDN call control layer specification, promulgated by the Consultative Committee on International Telephone and Telegraphy (CCITT)/International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) in the Q.931 call control layer specification. The capabilities described for each participant includes the bearer capability, low layer capability, and high layer capability.
In a system such as the Global System for Mobil Communications (GSM) network, a subset of the call control layer specification is used. Thus, each participant only provides support for a portion of the capabilities listed in the Q.931 call control layer specification. However, each participant (i.e., either the mobile stations or the base stations in the GSM network), still transmits a complete profile, which lists all capabilities that the participant is able to support.
When a communications session is initiated, all parties will provide a full set of capabilities as defined by the call control layer specification. During call set-up negotiations, participants will transmit their communication capabilities. The system then arrives at a mutually agreed set of communication parameters by eliminating all non-supported capabilities. Typically, the information transferred for each participant consumes more than 30 bytes of bandwidth in the call control layer.
The transmission of complete profiles occupies bandwidth that would otherwise be conserved for transmission of data. In addition, for mobile stations in a GSM system, as transmission and receipt of information requires the mobile station participant to expend energy, battery life is shortened, resulting in the mobile station requiring frequent recharging or changing of the power source of the mobile station. Thus, what is desired is the reduction of call-setup traffic in systems that operate under requirements such as those contained in the Q.931 specification.